Light source device for an image forming apparatus

ABSTRACT

A light source device for use in an image forming apparatus and using a semiconductor laser is disclosed. The device needs a minimum of constituent parts and frees the individual part from dislocation in the event of assembly. A collimator lens included in the device is fixed in place by photo-curable adhesive. The device is low cost and highly accurate.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a light source device for use inan image forming apparatus and using a semiconductor laser.

[0002] A digital copier, laser printer, facsimile apparatus or similarimage forming apparatus extensively used today includes a light sourcedevice having a semiconductor laser and a collimator lens. Opticalcharacteristics required of the light source device include thedirectivity of laser light (optical axis characteristic) and theparallelism of a beam (collimation characteristic). To meet theserequirements, it is a common practice to adjust the relative position ofthe emission point of the laser and the collimator lens in thedirections of three axes (x, y and z). The positional accuracy isseverely restricted to below the order of microns. Therefore, the deviceusing the Laser and collimator lens must be capable of being adjusted inthe three axis directions and then fixed at its adjusted position.

[0003] When the collimator lens is fixed in place by adhesive, theadhesive contracts in the event of setting. It is therefore necessary toreduce the influence of the contraction on the optical characteristicsas far as possible. Particularly, high accuracy is required of thedevice in the direction z (optical axis direction), so that thecontraction should preferably be prevented from occurring in thedirection z. For this purpose, the adhesive layer should preferablyextend substantially parallel to the optical axis (axis z). Also, thecontraction should preferably be limited to one of the directions X andy in order to facilitate adjustment even in such a direction.

[0004] Light source devices each having a semiconductor laser and acollimator lens are taught in, e.g., Japanese Patent Laid-OpenPublication Nos. 5-88061, 5-136952, and 5-273483. However, theconventional devices of the type described have some problems yet to besolved, as follows:

[0005] (1) Each device needs a number of constituent parts whichincrease the cost.

[0006] (2) The constituent parts are dislocated in the directions x, yand z in the event of assembly, so that the directivity (optical axischaracteristic) of the laser is deteriorated.

[0007] (3) Use cannot be made of ultraviolet light curable adhesive forfixing the collimator lens in place. This kind of adhesive can set in ashort period of time in a desired manner and is highly reliable.

[0008] The conventional devices have other problems which will bedescribed, in addition to the above problems.

SUMMARY OF THE INVENTION

[0009] It is therefore an object of the present invention to provide aninexpensive and highly accurate light source device needing a minimumnumber of constituent parts, protecting the individual part fromdislocation during assembly, and allowing a collimator lens to be fixedin place by photo-curable adhesive.

[0010] In accordance with the present invention, a light source devicehas a flat base member having a through bore. A semiconductor laser foremitting laser light is mounted on the rear of the base member andfitted in the through bore. A lens is mounted on the front of the basemember at the front of the through bore and coaxial with the opticalaxis of the semiconductor laser. A lens support member is positioned atthe front of the through bore coaxially with the optical axis of thesemiconductor laser. The lens support member has an arcuate section anda diameter slightly greater than the outside diameter of the lens. Thelens is affixed to the lens support member by photo-curable adhesive.

[0011] Also, in accordance with the present invention, a light sourcedevice has a base member having a through bore substantially at thecenter thereof. A semiconductor laser is fitted in the through bore foremitting laser light. A lens is mounted on the surface of the basemember. A lens support member supports the lens positioned in thedirections of three axes with adhesive filling a clearance between thelens and the surface of the base member.

[0012] Further, in accordance with the present invention, a light sourcedevice has a semiconductor laser for emitting laser light, a firstsupport member supporting the semiconductor laser, a lens positionedcoaxially with the optical axis of the semiconductor laser, and a secondsupport member supporting the lens. The first support member has a firstreference surface perpendicular to the optical axis of the semiconductorlaser. The second support member has a second reference surface parallelto the optical axis of the semiconductor laser.

[0013] Moreover, in accordance with the present invention, a lightsource device has a semiconductor laser for emitting laser light, afirst support member supporting the semiconductor laser, a lenspositioned coaxially with the optical axis of the semiconductor laser, asecond support member supporting the lens, aperture forming memberhaving an aperture for shaping the laser light issuing from thesemiconductor laser, and a third support member supporting the apertureforming member on the second support member from below the secondsupport member. The first support member is positioned perpendicularlyto the optical axis while the second support member is located in frontof the first support member.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The above and other objects, features and advantages of thepresent invention will become apparent from the following detaileddescription taken with the accompanying drawings in which:

[0015]FIG. 1 is a vertical section showing a conventional light sourcedevice;

[0016]FIG. 2 is an external perspective view showing anotherconventional light source device;

[0017]FIG. 3 is a vertical section showing a first embodiment of thelight source device in accordance with the present invention;

[0018]FIG. 4 is an exploded perspective view of the first embodiment;

[0019]FIG. 5 is a front view of a collimator lens and a lens supportportion also included in the first embodiment;

[0020]FIG. 6 is a section of the collimator lens and lens supportportion shown in FIG. 5;

[0021] FIGS. 7-13 are sections each showing a particular configurationof non-adhesion portions included in the lens support portion;

[0022]FIG. 14 is a vertical section showing a second embodiment of thepresent invention;

[0023]FIG. 15 is a vertical section showing a third embodiment of thepresent invention;

[0024]FIG. 16 is a section along Line XVI-XVI of FIG. 15;

[0025]FIG. 17 is a vertical section showing a fourth embodiment of thepresent invention; and

[0026]FIG. 18 is a plan view of the fourth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] To better understand the present invention, a brief referencewill be made to a conventional light source device of the type having asemiconductor laser and a collimator lens, shown in FIG. 1. This type oflight source device is taught in, e.g., previously mentioned JapanesePatent Laid-Open Publication No. 5-88061.

[0028] As shown in FIG. 1, the light source device has a base or supportmember 101 formed with a stepped through bore 102. A semiconductor laser103 for emitting laser light is press fitted in tie bore 102. For thebase 101, use is made of resin for low cost or of aluminum or similarmetal for precision, as needed. A flange 105 is fastened to the base 101by two screws 104. A bore 106 is formed in the flange 105 in alignmentwith the bore 102 of the base 101. The bore 106 merges into an inletportion 106 a located at the left-hand side of the bore 106, as viewedin FIG. 1. The inlet portion 106 a is about 1 mm greater in diameterthan the bore 106. A hollow cylindrical lens holder 107 is received inthe bore 106 and spaced from the wall of the bore 106 by a clearance ofabout 0.01 mm to 0.03 mm. A collimator lens 108 is fixed in place in thelens holder 107 in order to transform the laser light to a parallelbeam.

[0029] A printed circuit board 109 is formed with positioning holes 110.Guide pins 111 protruding from the end of the base 101 are respectivelyreceived in the holes 110. The tips of the guide pins 111 are deformedby heat, as indicated by dash-and-dots lines in FIG. 1. As a result, thebase 101 and circuit board 109 are affixed together. Leads 112 extendingout from the laser 103 are passed through lead holes formed in thecircuit board 109 and soldered to a conductive wiring pattern formed onthe rear of the circuit board 109. If the base 1201 is made of metal,then the guide pins 111 will be replaced with threaded holes formed inthe end of the base 101. In this case, the base 101 and circuit board109 will be fastened to each other by screws.

[0030] The flange 105 is accurately positioned such that the emissionpoint of the laser 103 aligns with the optical axis of the collimatorlens 108. In this condition, the flange 105 is fastened to the base 101by the screws 104. The flange 105 has a notch 113 communicated to theinlet portion 106 a. After the lens holder 107 has been positioned inthe direction z such that the emission point of the laser 103 coincideswith the focus of the collimator lens 108, adhesive is introduced intothe flange 105 via the notch 113. As a result, the lens holder 107 isaffixed to the flange 105 by the adhesive.

[0031] An aperture forming member 114 plays the role of a shield cap forseparating the central parallel part of the beam transmitted through thecollimator lens 108, i.e., for thereby shaping the beam. The apertureforming member 114 has an aperture 114 a for shaping the beam, and aprojection 114 b. The member 114 is affixed to the flange 105 with itsprojection 114 b mating with the notch 113.

[0032] When the above light source device is mounted to the body of acopier, laser printer or similar image forming apparatus, a flat surface105 a included in the flange 105 and perpendicular to the optical axisis used as a reference surface. The surface 105 a is also used as areference for the adjustment of optical characteristics.

[0033]FIG. 2 shows another conventional light source device taught in,e.g., previously mentioned Japanese Patent Laid-Open Publication No.5-136952 or 5-273483. As shown, the light source device has a barrel 121holding a collimator lens 120. The barrel 121 is received in a holder122. A semiconductor laser 123 is mounted on a printed circuit board 124which is in turn affixed to a base 125. The base 125 is retained bypawl-like projections 122 d extending from the holder 122. Adhesive isintroduced into grooves 122 a and 122 b and a hole 122 c formed in theholder 122. As a result, the base 125 and barrel 121 are affixed to theholder 122 by the adhesive.

[0034] The conventional devices described above, particularly the deviceshown in FIG. 1, bas the following problems left unsolved.

[0035] (1) The adjustment in directions x and y (optical characteristic)and the adjustment in the direction z (collimation characteristic orfocal direction) are each effected by a respective structure. Thisincreases the number of structural parts and therefore the productioncost of the device.

[0036] (2) The outside diameter of the lens holder 107 and the insidediameter of the bore 136 of the flange 105 must have strict accuracy.This increases the production cost of the lens holder 107 and flange105.

[0037] (3) After the adjustment in the directions x and y, the flange105 is fastened to the base 101 by the screws 104. Therefore, when thescrews 104 are driven into the flange 105 and base 101, screw seatsprovided on the end of the base 101 and the flange 105 bite into eachother. This is apt to bring about dislocation in the directions x and y,thereby lowering the accuracy of the directivity (optical axischaracteristic) of the laser.

[0038] (4) Because the laser light issuing from the laser 103 has acertain spread, it is not always entirely incident to the collimatorlens 108. Lasers in general are restricted by legal safety standards. Itis preferable that a laser beam issuing from a laser be prevented fromleaking in directions other than the direction of an optical axis. Thisis true not only when the laser is in use but also when adjustment iseffected an the production line. Therefore, the flange 105 ad base 101must be made of materials which intercept the laser beam.

[0039] (5) The adhesive for affixing the lens holder 107 shouldpreferably be ultraviolet light curable. This kind of adhesive hardensrapidly in a desired manner and is therefore desirable from theproduction time and reliability standpoint. However, because the base101 and flange 105 are made of materials opaque to ultraviolet rays,ultraviolet rays cannot uniformly illuminate the entire adhesive eveneven if radiated via the clearance through which the adhesive has beenintroduced. This results in irregular hardening and unhardened portions.Consequently, strains ascribable to contraction caused by hardening actunevenly on the assembly, resulting in the dislocation of the tensholder 107 and the cracks of the structural parts. Materials opaque tothe laser light, which may be infrared rays or red light, issuing fromthe laser 103 arm, of course, opaque to ultraviolet rays having a longerwavelength than the laser light. Therefore, to transmit only ultravioletrays, there is needed a special filter or a special coating on theflange 105, increasing the cost to a noticeable degree. This obstructsthe use of the ultraviolet light curable adhesive.

[0040] (6) Because the adhesive exists on the entire periphery of thelens holder 107, i.e., in both the direction x and the direction y, thedirection of the contraction of the adhesive is not limited to thedirection x or y. As a result, the positional accuracy is irregular inthe directions x and y. To guarantee the positional accuracy after theadhesion, it is necessary to provide the initial position with an offsettaking account of a certain degree of contraction. However, because thedirection of contraction is not fixed, it is difficult to implement theoffset. This sometimes lowers the accuracy of the directivity of thelaser (optical axis characteristic).

[0041] (7) Because the adhesive is introduced via the notch 113, it isapt to partly solidify or contract or to flow in an irregular finer. Asa result, a strain occur in the optical axis direction (direction z) andrenders positional accuracy irregular.

[0042] (8) The light source device is disposed in the body of an imageforming apparatus. Because the temperature in the apparatus body isusually high, the device is also subjected to high temperature duringthe course of operation. This, coupled with the fact that the laser 103itself generates heat, elevates the temperature of the device. Theprerequisite is therefore that the relative position of the laser 103and lens 108 adjusted in the directions x, y and z be surely held in acertain range even at high temperatures. Particularly, the displacementin the direction of optical axis (direction z) is severely restricted.Under these circumstances, if the base 101 is formed of ordinary resinto meet the cost reduction requirement, then its heat radiation abilityis lowered and deteriorate the characteristic of the entire assembly ina high temperature environment. Furthermore, the portions of the base101 and flange 105 fastened by the screws 104 are not strong, so thatthe relative position of the laser 103 and lens 108 is apt to vary dueto the fastening torque. Particularly, when a thermal stress is appliedto the assembly, the base 101, flange 105 and screws 104 each expands toa particular degree due to the respective coefficient of thermalexpansion. As a result, after the application of the thermal stress, thefastening stress and therefore the relative position of the laser 103and lens 108, i.e., the collimation characteristic is apt to vary. Inlight of this, the base 101, flange 105 and screws 104 may all be formedof the same material having a single coefficient of linear expansion.However, if the base 101 and flange 105 are formed of resin, the screws104 must also be formed of the same resin, resulting in an increase incost.

[0043] (9) The laser 103 for the light source device is provided withvarious kinds of configurations, depending on the configuration of animage forming apparatus, among others.

[0044] For example, a case surrounding the laser 103 may be used as apower source terminal (e.g. 5V). In this case, however, the laser 103does not emit light when the case surrounding it is brought to theground level. It is therefore necessary to isolate the case from theground level not only when the device is assembled but also when it ismounted to the apparatus body. If the base 101 and flange 105 are formedof metal radiating heat efficiently, then the device must include aportion for insulating the case of the laser 103 because the entiredevice is conductive. In addition, the base 101, flange 105 and screws104 must be formed of the same metal at the sacrifice of cost, as statedin the above item (8).

[0045] (10) To adjust the focus of the collimator lens 108 (directionz), the parallelism (collimation characteristic) of the laser beamshaped by the aperture 114 a is detected. Generally, because the laserbeam coming out of the aperture 114 a tends to spread due todiffraction, the parallelism of the beam differs from the case includingthe aperture 114 a to the case lacking it. Further, the degree ofparallelism depends on the characteristic of the individual laser 103.The parallelism of the laser beam necessary for the light source deviceis the characteristic of the beam coming out of the aperture 114 a; thatis, the light transmitted through the peripheral portion of the lens 108is not necessary. The peripheral portion of the lens 108 is noticeablyeffected by aberration and greatly differs from one lens to anotherlens. Therefore, even when the parallelism of the entire beam isdetected and satisfies the required accuracy, it is sometimesunsatisfactory when it comes to the part of the beam around the center.It follows that ideally the focus of the lens 108 should be adjustedafter the aperture forming member 114 has been mounted. However, becausethe aperture forming member 114 covers the lens 108, the leas 108 cannotbe adjusted after the mounting of the aperture 114 a. As a result, theparallelism of the laser beam varies after the mounting of the aperture114 a.

[0046] (11) The light source device is fastened to the apparatus body byscrews with the surface 105 a of the flange 105 serving as a reference.Screws are driven into the reference surface 105 a from above theapparatus body or from one side of the apparatus body, depending on theconfiguration of the apparatus body. However, the device can be fastenedonly from the side of the apparatus body because the reference surface105 a is perpendicular to the optical axis of the laser beam. When theflange 105 must be fastened from above the apparatus body, anintermediary mounting member is required. This not only increases thecost but also lowers the accuracy of optical axis characteristic due tothe intermediary member. As a result, the device lacks ingeneral-purpose applicability. This is also true with the light sourcedevice shown in FIG. 2 because it is configured to be mounted from abovethe apparatus body.

[0047] (12) The laser 103 is easily deteriorated or damaged by staticelectricity or similar electrical noise. Ideally therefore, the deviceshould be assembled and adjusted fully automatically so as to beisolated from static electricity issuing from the human body. Theautomatic assembly and adjustment will save labor cost and will improvequality and yield of products. In an automatic machine, the referencesurface for setting workpieces including light source devices shouldadvantageously be horizontal, considering the loading and unloading ofthe workpieces. When the production of the light source device havingthe reference surface 105 a perpendicular to the optical axis isautomated, it should preferably be set face down (causing the laser beamto issue downward) in order to facilitate the production. However, sucha configuration requires the adhesive to be introduced into the assemblydownward or sideways after the adjustment of the collimator lens 108.This is not practical, considering the drop of the adhesive. Moreover,the aperture must be mounted to the assembly from below the assemblyafter the injection of the adhesive, complicating the automatic machineor requiring an extra step.

[0048] Preferred embodiments of the light source device in accordancewith the present invention will be described which are free from theproblems discussed above.

1st Embodiment

[0049] Referring to FIGS. 3-13, a light source device embodying thepresent invention is shown. As shown in FIGS. 3 and 4, the device has aprinted circuit board 1, a semiconductor laser 2, a flat base 3 forholding the laser 2, a collimator lens 4, and an aperture forming member5. In the illustrative embodiment, the base 3 is formed of insulatingresin having a coefficient of linear expansion of 2.3×10⁻⁵/K or below,as measured in the optical axis direction, and a thermal conductivity of0.9 W/m.K or above. This kind of resin surely provides the base 3 with acollimation characteristic and a heat radiation characteristic againstchanges in temperature. For example, use may be made of unsaturatedpolyester resin containing glass fibers and satisfying the aboveconditions. The base 3 is opaque to an infrared laser beam issuing fromthe laser 2 (e.g. 780 nm) and light shorter in wavelength than the same.

[0050] A stepped through bore 3 a is formed throughout substantially thecenter of the base 3. The a 2 is press fitted in the bore 3 a from therear of the base 3. Because unsaturated polyester resin with glassfibers and constituting the base 3 is insulative, a case surrounding thelaser 3 and mounted to the base 3 is fully electrically insulated. Thiseliminates the need for special insulation otherwise provided on thecase of the laser 2.

[0051] Two spacers 3 b protrude from the rear of the base 3, and each isformed with a threaded bore 3 c for affixing the printed circuit board1. Two through holes 1 a are formed in the circuit board 1 in alignmentwith the spacers 3 b. Screws 6 are respectively driven into the threadedbores 3 c via the holes 1 a, thereby fastening the base 3 and circuitboard I together. If desired, the threaded boles 3 c and screws 6 may bereplaced with simple holes and tapping screws, respectively.

[0052] Three leads 2 a extending out from the laser 2 are respectivelypassed through lead holes 1 b formed in the circuit board 1 and aresoldered to a conductive wiring pattern provided on the rear of thecircuit board 1.

[0053] The collimator lens 4 is directly affixed to the base 3 byadhesive. For this purpose, a lens support portion 3 d is formedintegrally with the base 3 and coaxially with the optical axis of thelaser 2. The lens support portion 3 d is positioned at the front of thebore 3 a and provided with an arcuate section. This portion 3 d isslightly greater in diameter (e.g. about 0.3 mm) than the outsidediameter of the collimator lens 4. As shown in FIG. 7, the lens supportportion 3 d has a length in the optical axis direction (direction z)great enough to form non-adhesion pons G1 and G2. Even when adhesive gis applied in an excessive amount, the portions G1 and G2 prevent itfrom depositing on the other portions. This will be describedspecifically later. The arc of the lens support portion 3 d is smallerthan a semicircle, as seen from the front.

[0054] As shown in FIG. 5, the arc of the lens support portion 3 d asviewed in a section should preferably extend over an angle of about 60degrees and be symmetrical in the right-and-left direction.

[0055] The collimator lens 4 is formed of a material transparent toultraviolet rays. While the lens 4 may be implemented as a plastic lensor a glass lens, a glass lens is superior to a plastic lens as tooptical characteristic. As shown in FIG. 5, in the event of assembly,the lens 4 is held by a chuck 7 adjustable in position in the directionsx, y and z. Then, the lens 4 is positioned on the lens support portion 3d coaxially with the laser 2. Subsequently, the ultraviolet lightcurable adhesive 8 is filled in the clearance between the surface 3 e ofthe lens support portion 3 d and the outer periphery of the lens 4.Thereafter, the position of the lens 4 is finely adjusted while havingits optical characteristic monitored by a testing device, not shown. Assoon as the lens 4 is brought to a position where it obtains a desiredoptical characteristic, the chuck 7 is fixed in place there. Then, asshown in FIGS. 5 and 6, an ultraviolet radiator 9 radiates ultravioletrays L toward the adhesive 8 from above the collimator lens 4. Theultraviolet rays L are incident to the adhesive 8 by way of the lens 4and causes it to set uniformly. As a result, an adhesive layer ofuniform thickness and symmetrical in the right-and-left direction isformed between the surface 3 e of the support portion 3 d and the lens4. The adhesive layer has a thickness equal to the gap between thesurface 3 e and the lens 4 (about 0.3 mm). The lens 4 is affixed to thesupport portion 3 d by the adhesive layer while maintaining the desiredoptical characteristics.

[0056] Particularly, the arcuate section of the lens support portion 3 dwhich extends over about 60 degrees, as shown in FIG. 5, has thefollowing advantage. The chuck 7 can support the collimator lens 4surely and easily. Because the ultraviolet rays L issuing from theradiator 9 are uniformly incident to the entire surface 3 c via the lens4, the adhesive 8 can set evenly over its entire area. Such a uniformand fully set adhesive layer prevents the lens 4 from being displaceddue to irregular hardening and unhardened portions.

[0057] Further, strains ascribable to contraction of the adhesive 8occur symmetrically in the direction x (right-and-left direction) andtherefore cancel each other. As a result, a strain occurs only in thedirection y (up-and-down direction). It is therefore possible to providethe initial position of the collimator lens 4 with a slight offset inthe direction y before hardening, taking account of the contraction.This enhances the accuracy in the optical characteristic of the lens 4after fixation.

[0058] The base 3 is formed of an insulating material having aparticular coefficient of linear expansion in the axial direction and aparticular thermal conductivity, as stated earlier. Despite that thelaser 2 generates heat, the great thermal conductivity of the base 3allows the temperature of the light source device to rise only about 5°C. at most above the temperature inside the apparatus body. Moreover,the coefficient of Linear expansion of the base 3 is as small as that ofaluminum. Hence, even if the temperature of the light source devicerises about 5° C., it does not cause the relative position of the laser2 and lens 4 to change noticeably. In addition, the collimationcharacteristic of the leas 4 is held stable against changes intemperature.

[0059] As shown in FIGS. 3 and 4, the base 3 additionally has an annularstepped portion 3 h at the root of the lens support portion 3 d. Thestepped portion 3 h has at its end an annular recess 3 k concentric withthe bore 3 b and greater in diameter than the collimator lens 4. Therecess 3 k is deep enough to prevent the adhesive g from depositing onthe surface of the stepped portion or base wall 3 h when the adhesive 8spreads more than the expected degree. Specifically, as shown in FIG. 7,the previously mentioned non-adhesion portion (G1 is formed between thesurface of the base wall 3 h and the lens 4. Further, the tip of thesupport portion 3 d extends forward sufficiently over the lens surfaceof the lens 4, so that even the adhesive 8 spread excessively toward thetip of the support portion 3 d will not drop. Specifically, as shown inFIG. 7, the previously mentioned non-adhesion porous G2 is formedbetween the tip of the support portion 3 d and the lens 4.

[0060] Assume that the adhesive 8 is filled in the gap between thecollimator lens 4 and the support portion 3 d in an excessive amount.Then, the non-adhesion portions G1 and G2 sandwiching the lens 4 preventthe adhesive 8 from depositing and solidifying on the surface of thebase wall 3 h or from solidifying while dropping from the tip of thesupport portion 3 d, as shown in FIG. 8. Assume that the above portionsG1 and G2 are absent. Then, as shown in FIG. 9, the adhesive 9 fed in anexcessive amount deposits and solidifies on the surface of the base wall3 h and solidifies while dropping from the tip of the support portion 3d. As a result, the contraction force of the adhesive 8 derived fromhardening and acting in the optical axis direction (direction z) isdirectly exerted on the lens 4 and dislocates it.

[0061] As shown in FIG. 9, the contraction force of the adhesive 8acting on the base wall 3 h, as mentioned above, is extremely strongbecause it acts on the lens surface of the collimator lens 4 directlyand perpendicularly thereto. By contrast, the adhesive 8 solidified atthe tip of the support portion 3 d depends from the tip and does notdirectly contact the lens surface. Therefore, the force of this part ofthe adhesive 8 is not critical. In light of this, the non-adhesionportion G2 terminating at the tip of the lens support portion 3 d may beomitted, depending on the accuracy required of the light source device.

[0062] Referring again to FIGS. 3 and 4, the aperture forming member 5has an aperture 5 a and two pairs of lugs 5 b and 5 c for affixing themember 5 to the base 3. On the other hand, the base 3 has two pair ofarcuate positioning grooves 3 f and 3 g. After the collimator lens 4 hasbeen fixed in place by the previously sated procedure, the apertureforming member 5 is positioned such that its lug pairs 5 b and 5 crespectively face the groove pairs 3 f and 3 g of the stepped portion 3h of the base 3. Then, the member 5 is pushed toward the base 3. As aresult, the lug pairs 5 b and 5 c respectively mate with the groovepairs 3 f and 3 g, affixing the member 5 to the base 3.

[0063] Two slots 3 i are formed at the right and left end portions ofthe base 3 and used to mount the light source device to a digitalcopier, laser printer or similar image forming apparatus. At thisinstant, the vertical surface or front 3 j of the base and the outercircumferential surface of the stepped portion 3 h are used as areference for positioning.

[0064] FIGS. 10-13 each shows another specific configuration of thenon-adhesion portions G1 and G2. The configuration shown in FIG. 10lacks the annular recess 3 k and simply increases the distance betweenthe surface of the stepped portion 3 h and the collimator lens 4 and thedistance between the tip of the Ices support portion 3 d and the lens 4.This is the simplest configuration.

[0065] The configuration shown in FIG. 11 is a modification of theconfiguration of FIG. 10. As shown, an upright wall 3 m extends from thetip of the surface 3 e of the support portion 3 d. The wall 3 m surelyprevents the excessing portion of the adhesive 8 from spreading over thetip of the support portion 3 d.

[0066]FIG. 12, a table portion 3 n having a width substantiallyidentical with the thickness of the lens 4 is formed on the surface 3 eof the support portion 3 d. The lens 4 is adhered to the table portion 3n. In this configuration, the excessive part of the adhesive 8 isreceived in stepped portions located at both sides of the table 3 n.Therefore, even when the adhesive 8 is fed in an excessive amount, itscontraction force does not directly act on the lens surface so long asthe the adhesive 8 received in the stepped portions does not rise abovethe lower edge of the lens 4.

[0067] The configuration shown in FIG. 13 is a modification of theconfiguration of FIG. 12. As shown, the table portion 3 n shown in FIG.12 is combined with the upright wall 3 m shown in FIG. 1. This alsoprevents the adhesive 8 from spreading over the tip of the supportportion 3 d.

[0068] While the adhesive 8 of the illustrative embodiment isultraviolet light curable adhesive, it is only illustrative and may bereplaced with any other adhesive so long as it is photo-curable.

[0069] The embodiment described above has the following advantages.

[0070] (1) Because a collimator lens is directly affixed to a lenssupport portion formed integrally with a base, a light source deviceneeds a minimum number of parts and is low cost. Further, the devicedoes not include any portion to be fastened by screws and thereforefrees its structural parts from displacement due to fastening, therebyachieving high accuracy.

[0071] (2) The device allows the collimator lens to be fixed by place byphoto-curable adhesive despite that it prevents light issuing from asemiconductor laser from leaking in directions other than the opticalaxis direction.

[0072] (3) The collimator lens is adhered to the lens support portionhaving an arcuate shape by the photo-curable adhesive. This allowssetting light to be radiated toward the adhesive layer from above thelens, thereby setting the adhesive. Because the support portion and theoptical axis of the laser are coaxial, the adhesive layer formed betweenthe support portion and the lens has a uniform thickness and solidifiesevenly. Therefore, the device prevents the lens from being dislocateddue to the contraction of the adhesive in the event of hardening.

[0073] (4) Because the adhesive layer contacts only the lower half ofthe outer circumference of the lens, the contraction has directivity. Itis therefore possible to provide the initial position of the lens withan offset, taking account of a certain degree of contraction. Thisenhances the positional accuracy of the lens after it has been fixed inplace. Because the setting or curing light can be easily radiated fromabove the lens, the irregular hardening is further obviated, and thepositional accuracy is further enhanced.

[0074] (5) Sums due to the contraction and acting in the right-and-leftdirection (direction x) are symmetrical and cancel each other. Thislimits the contraction only to the up-and-down direction (direction y)and thereby further improves the directivity of the contraction.Consequently, the device can be adjusted more accurately.

[0075] (6) A non-adhesion portion intervenes between the wall of thebase and the lens. Even when the adhesive is fed in an excessive amount,the non-adhesion portion prevents it from directly depositing on thewall of the base; otherwise, the excessive developer would deposit andsolidify on the wall of the base and exert an intense contraction forceon the lens in the optical axis direction (direction z). This enhancesaccurate positioning in the optical axis direction.

[0076] (7) Another non-adhesion portion intervenes between the lens andthe tip of the lens support portion. This non-adhesion portion preventsthe adhesive from spreading as far as the tip of the support portion andsolidifying there. This further enhances accurate positioning in theoptical axis direction.

[0077] (8) The base for mounting the laser and lens thereon is formed ofinsulating resin having a coefficient of linear expansion of 2.3×10⁻⁵/Kor below in the optical axis direction, and a thermal conductivity of0.9 W/m.K or above. Therefore, despite that the laser generates heat,the temperature of the device rises only slightly above the temperatureinside the body of an image forming apparatus. Moreover, such atemperature elevation does not cause the relative position of the laserand lens to change noticeably. Consequently, a stable collimationcharacteristic is maintained against changes in temperature.

[0078] (9) Because the base itself is insulative, a case surrounding thelaser is fully electrically insulated without resorting to any specialinsulating structure. The device is therefore simple and low cost.

2nd Embodiment

[0079] Referring to FIG. 14, an alternative embodiment of the presentinvention will be described. As shown, the light source device has abase or support member 15 formed with a stepped through bore 16substantially at its center. A semiconductor laser 12 is press fitted inthe bore 16. The base 15 is formed of a substance opaque to infraredrays (about 780 nm) and light having shorter wavelengths. The base 15has on its outer surface a first cylindrical surface 18 and a secondcylindrical surface 17 smaller in diameter than the cylindrical surface18. A guide pin 11 protruding from the right end of the base 15, asviewed in FIG. 14, is passed through a positioning hole 10 a formed in aprinted circuit board 10, and then affixed to the circuit board 10 bythermal deformation. The laser 12 and circuit board 10 are electricallyconnected together by leads 12 a.

[0080] A collimator lens 19 is formed of a material transparent toultraviolet rays. While the lens 19 may be implemented as a plastic lensor a glass lens, a glass lens is superior to a plastic lens as tooptical characteristic. The lens 19 has at its right end, as viewed inFIG. 14, a recess 20 for forming a clearance of about 0.5 mm (at eachside) between the lens 19 and the smaller diameter cylindrical surface17. In this condition, when the cylindrical surface 17 is loosely fittedin the recess 20, the clearance allows the lens 19 to be adjusted in thedirections x and y.

[0081] A method and a structure for supporting the collimator lens 19 onthe base 15 are as follows. The lens 19 is held by a chuck, not shown,movable in the directions x, y and z, and then finely adjusted in theabove three directions with the optical characteristic of the laser beambeing monitored. After the lens 19 has been fully positioned, anultraviolet radiator 22 radiates ultraviolet rays toward the assembly.Adhesive 21 is filled in the clearance between the cylindrical surface17 and the lens 19 either entirely or at a plurality of positions. Theultraviolet rays cause the adhesive 21 to solidify in a short period oftime. As a result, the lens 19 is affixed to the base 15. Of course, thethickness of the adhesive or adhesive layer 21 depends on the lightsource device. An aperture forming member 14 having an aperture 14 a ispress fitted on the cylindrical surface 18.

3rd Embodiment

[0082]FIGS. 15 and 16 show another alternative embodiment of the presentinvention d FIGS. 15 and 16, structural elements identical with theelements shown in FIG. 14 are designated by identical referencenumerals. As shown, the light source device has a base or support member23 formed of the same material as the base 15, FIG. 14. Thesemiconductor laser 12 is press fitted in the through bore 15 formed inthe base 23. The guide pin 11 protruding from the right end of the base23 is received in the hole 10 a of the printed circuit board 10 and thendeformed by heat. As a result, the circuit board 10 is affixed to thebase 23. The aperture forming member 14 is press fitted on thecylindrical surface 18 of the base 23. The configuration described sofar is identical with the configuration shown in FIG. 14.

[0083] In this embodiment, the smaller diameter cylindrical surface 18is replaced with a recessed surface 24 contiguous with the greaterdiameter cylindrical surface 18. A cylindrical collimator lens 25 as nouter circumferential surface substantially parallel to the recessedsurface 24. When the lens 25 is held by a chuck, not shown, movable inthe directions x, y and z, a clearance of about 0.5 mm is formed betweenthe lens 25 and the recessed surface 24.

[0084] The lens 25 is formed of the same material as the lens 19 of thesecond embodiment. The lens 25 is finely adjusted in the directions x, yand z with the optical characteristic of the laser beam being monitored.Subsequently, the adhesive 21 is filled in the clearance between thelens 25 and the surface 24. The ultraviolet radiator 22 radiatesultraviolet rays toward the assembly in order to cause the adhesive 21to solidify in a short period of time. As a result, the lens 25 isaffixed to the base 23 by the adhesive 21.

[0085] As stated above, the second and third embodiments described abovehave the following advantages.

[0086] (1) Because a collimator lens is adjustable in three differentdirections (x, y and z), a single adjusting portion suffices. Thisreduces the number of structural parts of the light source device.

[0087] (2) Because a substantial clearance is available between the lensand a support member, the accuracy required of the individual part is e;Hence, the light source device is low cost.

[0088] (3) The decrease in the number of parts obviates portions to befastened by screws. This frees the parts from dislocation ascribable tofastening and enhances the accuracy of the device.

[0089] (4) Adhesive is hardened by ultraviolet rays transmitted throughthe lens. Hence, despite the structure preventing a laser beam fromleaking in directions other than the optical axis direction, it ispossible to illuminate the adhesive uniformly and cause it to fullyharden. This obviates changes in the adhesive due to aging and frees itfrom irregular hardening and unhardened portions.

4th Embodiment

[0090] Referring to FIGS. 17 and 18, a further alternative embodiment ofthe present invention will be described. As shown, the light sourcedevice has a semiconductor laser 32 for emitting laser light, acollimator leas 38 for collimating the laser light to output asubstantially parallel beam, and a base or support member 35 supportingthe laser 33. The base 35 is formed of a material opaque to light havingwavelengths shorter than about 780 mm (infrared rays) inclusive.

[0091] The laser 33 is press fitted in a stepped through bore 35 aformed in substantially the center of the base 35. A pair of spacers 35b are formed integrally with the base 35. Guide pins 35 c each protrudesfrom the respective spacer 35 b. A printed circuit board 30 is formedwith positioning holes 30 a slightly smaller in diameter than the guidepins 35 c. The base 35 is affixed to the circuit board 30 with its guidepins 35 received in he positioning holes 30 a. After the base 35 hasbeen affixed to the circuit board 30, leads 33 a extending out from thelaser 33 are respectively passed through holes 30 b formed in thecircuit board 30. Then, the leads 33 a are soldered to a conductivewiring pattern provided on the rear of the circuit board 30.

[0092] An aperture forming member 36 for forming an aperture 36 a isparty cut and bent to form an elastic tongue 36 b. The aperture formingmember 36 is received in a groove 35 d formed in the base 35 and isfixed in place due to the elasticity of the tongue 36 b. The base 35 hasa recessed surface 35 e. A collimator lens 38 has a contoursubstantially parallel to the recessed surface 35 e. The lens 38 is heldby a chuck, not shown, adjustable in position in the directions x, y andz. A clearance of about 0.5 mm is formed between the collimator lens 38and the surface 35 e and filled with adhesive 31.

[0093] The collimator lens 38 is formed of a material transparent toultraviolet rays. While the lens 38 may be implemented as a plastic lensor a glass lens, a glass lens is superior to a plastic lens in respectof optical characteristic. After the aperture forming member 36 has beenaffixed to the lens 39, it is finely adjusted in the directions x, y andz while the optical characteristic of the laser beam issuing via theaperture 36 a is monitored. Then, the adhesive is filled in theclearance between the lens 38 and the surface 35 c of the base 35.Subsequently, an ultraviolet radiator 32 radiates ultraviolet raystoward the assembly in order to cause the adhesive 31 to solidify in ashort period of time. Because the lens 38 is transparent to ultravioletrays, the adhesive 31 solidifies evenly and adheres the leas 38 to thebase 35 while maintaining its collimation characteristic.

[0094] Assume that the above light source device is mounted to the bodyof a digital copier, laser printer or similar image forming apparatus orto a host unit. The base 35 is generally L-shaped and has a firstreference surface 35 f parallel to the optical axis, and a secondreference surface 35 g perpendicular to the optical axis. To mount thedevice to the apparatus body or the host unit from above the apparatusbody, the device is positioned in the direction of rotation (directionsx and y) by use of two positioning holes 35 h. Then, screws are driveninto two threaded holes 35 i from above the device in order to fastenthe device to the apparatus body with the first reference surface 35 fcontacting the reference surface of the apparatus body. To mount thedevice to the apparatus body from one side of the apparatus body, thedevice is positioned in the direction of rotation (directions x and y)by use of two positioning holes 35 i and then fastened to the side ofthe apparatus body via two threaded holes 35 k. In this case, the secondreference surface 35 g contacts the reference surface of the apparatusbody.

[0095] The light source device may be assembled and adjusted by anautomatic machine by the following procedure. First, the base 35 ispositioned such that its second reference surface 35 g extendshorizontally. Then, the leads 33 a of the laser 33 an soldered to theconductive wiring pattern of the circuit board 30 from above the circuitboard 30. The optical characteristic of the device is adjusted with thefirst reference surface 35 f held in a horizontal position. The steps ofinserting the aperture forming member 36, applying the adhesive 31,positioning the collimator lens 38, radiating ultraviolet rays are alleffected from above the device, so that the automatic assembly isfacilitated.

[0096] Of course, the first and second reference surfaces 35 f and 35 gmay each be implemented by a respective support member. The apertureforming member 36 and collimator lens 38 may be aced to a single member,or each may be affixed to a respective member. The member or members towhich the member 36 is affixed may be formed integrally with orseparately from the base 35. Even when the surface where the lens 38 islocated is different from the horizontal reference surface, it does noteffect the collimation characteristic of the lens 38 because the lens 38is affixed to the base 35 after the optical characteristics of the lens38 including the collimation characteristic have been examined.

[0097] The fourth embodiment described above has the followingadvantages.

[0098] (1) The light source device has a first and a second referencesurface respectively perpendicular and parallel to the optical axis of asemiconductor laser. A collimator lens is fixed in place with itsoptical axis aligned with that of the laser. Hence, the device can bereadily mounted to an apparatus body or host unit without having itscollimation characteristic deteriorated.

[0099] (2) Because a base is implemented as a single molding, the deviceneeds a minimum number of parts and is therefore low cost.

[0100] (3) The decrease in the number of parts obviates portions to befastened by screws. This eliminates the dislocation of the individualpart ascribable to fastening using screws and thereby provides thedevice with high accuracy.

[0101] (4) Ultraviolet light curable adhesive is solidified byultraviolet rays transmitted through the lens. It is therefore possibleto fully harden the adhesive by uniform radiation, and therefore toobviate irregular hardening and unhardened portions.

[0102] (5) Light issuing from the laser does not leak in directionsother than the optical axis direction, so that the adhesive is free fromvariation ascribable to aging.

[0103] (6) The focus of the lens can be adjusted after an apertureforming member has been mounted. This prevents the opticalcharacteristic from being varied after the mounting of the apertureforming member.

[0104] (7) Because the device has the first and second referencesurfaces respectively perpendicular and parallel to the optical axis ofthe laser, it can be mounted to an apparatus body or host unit fromabove or from one side of the apparatus body, as desired. This providesthe device with general-purpose applicability.

[0105] (8) The first reference surface allows the mounting of theaperture forming member, the application of the adhesive, thepositioning of the lens and the radiation of ultraviolet rays to beeffected from above the device without exception. This facilitate theautomatic assembly and adjustment of the device.

[0106] Various modifications will become possible for those skilled inthe art after receiving the teachings of the present disclosure withoutdeparting from the scope thereof.

What is claimed is:
 1. A light source device comprising: a flat basemember having a through bore; a semiconductor laser mounted on a rear ofsaid base member and fitted in said through bore, and for emitting laserlight; a lens mounted on a front of said base member at a front of saidthrough bore and coaxial with an optical axis of said semiconductorlaser; and a lens support member positioned at the front of said throughbore coaxially with the optical of said semiconductor laser, and havingan arcuate section, and having a diameter slightly greater than anoutside diameter of said lens; wherein said lens is affixed to said lenssupport member by photo-curable adhesive.
 2. A light source device asclaimed in claim 1, wherein said lens support member is formedintegrally with said base member.
 3. A light source device as claimed inclaim 1, wherein said lens support member has an arc smaller than asemicircle.
 4. A light source as claimed in claim 1, wherein said lenssupport member has an arc symmetrical in a right-and-left direction. 5.A light source device as claimed in claim 1, further comprising anaperture forming member for shaping the laser light output from saidlens.
 6. A light source device as claimed in claim 1, wherein said lenscomprises a collimator lens.
 7. A light source device as claimed inclaim 1, wherein a non-adhesion portion is formed at least between saidlens affixed to said lens support member and a wall of said base member.8. A light source device as claimed in claim 7, wherein saidnon-adhesion portion comprises an annular recess formed in said wall ofsaid base member concentrically with said through bore.
 9. A lightsource device as claimed in claim 7, wherein said non-adhesion portioncomprises a groove having a width greater than a thickness of said lens.10. A light source device as claimed in claim 7, wherein saidnon-adhesion portion comprises a table portion having a lengthsubstantially identical with a thickness of said lens.
 11. A lightsource device as claimed in claim 7, wherein another non-adhesionportion is formed between said lens and a tip of said lens supportmember.
 12. A light source device as claimed in claim 1, wherein saidbase member comprises insulating resin having a coefficient of linearexpansion of less than 2.3×10⁻⁵ /K inclusive in a direction of theoptical axis, and a thermal conductivity of greater than 0.9 W/m.Kinclusive.
 13. A light source device comprising: a base member having athrough bore substantially at a center thereof; a semiconductor laserfitted in said through bore and for emitting laser light; a lens mountedon a surface of said base member; and a lens support member supportingsaid lens positioned in directions of three axes with adhesive filling aclearance between said lens and said surface of said base member.
 14. Alight source device as claimed in claim 13, wherein said base member isformed of a material opaque to light having wavelength shorter than awavelength of infrared rays (about 780 nm) inclusive, and wherein saidleas is formed of a material transparent to ultraviolet rays.
 15. Alight source device as claimed in claim 13, wherein said adhesivefilling said clearance forms a layer substantially parallel to anoptical axis.
 16. A light source device as claimed in claim 13, furthercomprising a printed circuit board electrically connected to saidsemiconductor laser and affixed to said base member.
 17. A light sourcedevice as claimed in claim 13, further comprising an aperture formingmember formed with an aperture for shaping the laser light output fromsaid lens, and mounted on said base member.
 18. A light source device asclaimed in claim 13, wherein said lens comprises a collimator lens. 19.A light source device comprising: a semiconductor laser for emittinglaser light; a first support member supporting said semiconductor laser;a lens positioned coaxially with an optical axis of said semiconductorlaser; and a second support member supporting said lens; wherein saidfirst support member has a first reference surface perpendicular to theoptical axis of said semiconductor laser, and wherein said secondsupport member has a second reference source parallel to the opticalaxis of said semiconductor laser.
 20. A light source device as claimedin claim 19, wherein said first and second support members are formedintegrally with each other.
 21. A light source device as claimed inclaim 19, further comprising an aperture forming member having anaperture for shaping the laser light issuing from said semiconductorlaser.
 22. A light source device comprising: a semiconductor laser foremitting laser light; a first support member supporting saidsemiconductor laser; a lens positioned coaxially with an optical axis ofsaid semiconductor laser; a second support member supporting said lens;an aperture forming member having an aperture for shaping the laserlight issuing from said semiconductor laser; and a third support membersupporting said aperture forming member on said second support memberfrom below said second support member; wherein said first support memberis positioned perpendicularly to the optical axis, and wherein saidsecond support member is located in front of said first support member.23. A light source device as claimed in claim 22, wherein said firstsupport member has a first reference surface implemented by a verticalsurface thereof for positioning said light source device relative to ahost unit, and wherein said second support member has a second referencesurface implemented by a bottom surface thereof for positioning saidlight source device relative to the host unit.
 24. A light source deviceas claimed in claim 22, wherein a surface for supporting said Lenscomprises a recessed surface.
 25. A light source device as claimed inclaim 22, wherein said aperture forming member is elastically supportedby said third support member.
 26. A light source device as claimed inclaim 22, wherein said first, second and third support members areformed integrally with each her.
 27. A light source device as claimed inclaim 22, wherein said first and second support members are configuredin a form of letter L.